Description

Allows to send parameter data to the server in pieces (or chunks), e.g. if the
size of a blob exceeds the size of max_allowed_packet.
This function can be called multiple times to send the parts of a character or
binary data value for a column, which must be one of the TEXT or BLOB datatypes.

send_long_data() these function is normaly used to store Data in Binary blob field. But if the table is UTF8 and connection charset it does not expect binary data (for example images) it take utf8 Data.
This mean you have to do utf8_encode bevore sending binary data.